B.S. Sharif University of Technology, Iran

Ph.D. Washington University, St Louis

Biological Chemistry Program

Enveloped Virus Budding

Research

My lab is focused on development of microscopy techniques which will merge live imaging
and high resolution microscopy, visualizing many of the essential molecular mechanisms
critical for the function of retroviruses specifically HIV as well as negative strand
RNA viruses specifically VSV. Our current microscopy focus is to extend capabilities
of the iPALM microscopy for single molecule tracking and high resolution imaging of
virological samples. We are especially keen in applying the fluctuations based methodologies
as well as high resolution imaging to better understand transport and molecular mechanisms
driving the biological mechanisms in VSV replication and HIV budding and maturation.

HIV Budding and Maturation

Our long-term goal is to gain a molecular understanding of the machinery that regulates
the release of infectious HIV virions from infected cells. Newly released HIV virions
are immature and non-infectious. The immature HIV lattice is composed of ~120 copies
of Gag-Pol along with ~2000 copies of Gag. The immature virion incorporates the HIV
protease as a monomer within the Gag-Pol precursor. During budding, HIV recruits members
of the Endosomal Sorting Complexes Required for Transport to help catalyze its release
from host cells. It is believed that sometime after release of virions, HIV protease
monomers are released from the confines of the Gag-Pol proteins and form active protease
dimers which in turn drive the transformation of the immature lattice to infectious
mature HIV core. During the past couple of years, we evaluated the exact role of early
Endosomal Sorting Complexes Required for Transport (ESCRT), ALIX and TSG101, in HIV
budding. We found that these early ESCRTs play a major role in a molecular race between
virion budding and activation of HIV protease which is essential for virion maturation
and infectivity. Currently we are interested in understanding the exact molecular
mechanism by which ESCRTs catalyze the release of HIV virions. We are also interested
in understanding the molecular mechanism that drives the process of maturation specifically
initiation of protease release from Gag-Pol molecules and the relation of these molecular
events to virion release.

Negative strand non-segmented (NNS) RNA viruses include potent human and animal pathogens,
e.g. Ebola, measles and vesicular stomatitis virus (VSV). To transcribe and replicate
their genome, these viruses package multiple copies of an RNA dependent RNA polymerase
(RdRP), within each virion. While the virion morphology varies among NNS RNA viruses,
the basic mechanism of transcription and replication is shared. Specifically, the
genome template in NNS RNA viruses consists of a single molecule of negative sense
RNA, typically encoding more than 5 genes and fully encapsidated with the nucleoprotein
N (N-RNA). RdRP polymerases transcribe the genome sequentially by initiating transcription
at or near the 3' end and moving toward the 5' end. While the N-RNA bound with RdRPs
is the deadly engine within many major human pathogens, it’s transcription mechanism
is distinct from cellular DNA based RNA polymerases and remains poorly understood.
We are focused on establishing a fundamental understanding of the RdRP transcription
and open the door to its further applications.

Artistic rendering of Vesicular Stomatitis Virus during RNA capture at the plasma
membrane. For simplicity only the N molecule is shown. The illustrated packing within
the virion is consistent with Cryo EM studies of VSV. The extended spiral outside
the formed virion is an artistic expression. It is not clear for how long the RNA
would retain its spiral twist in the cytoplasm.